In various apparatus, for example pumps, blowers, mixers, or other processing equipment where a rotatable shaft is provided with associated impellers to move a fluid, it is necessary to provide shaft seals to prevent leakage of the fluid from around the moving member. Seals are particularly necessary when the device handles expensive or hazardous fluids or where the fluid is processed at elevated pressure.
Three common seal arrangements are generally utilized, as known in the art, including stuffing boxes, mechanical seals and labyrinths. None of the devices completely prevents leakage but are effective to minimize or control leakage. In other arrangements where leakage of the fluid in process cannot be tolerated an innocuous fluid can be provided to the seal to flow into the process.
The present invention while useful in some degree in all of the aforementioned sealing arrangements is particularly useful in stuffing boxes which provide a seal around a rotating shaft or in some cases a reciprocating shaft. The stuffing box is, generally, a chamber located in a stationary member that surrounds the shaft. An annular space is provided between the shaft and the wall of the chamber through which the shaft passes, and the annular space is adapted to receive packing which can include rope or rings of inert material such as, for example, asbestos containing a lubricant like graphite. The packing, when compressed tightly around the shaft, discourages fluid passage through the stuffing box and yet permits the shaft to turn or reciprocate. In many applications, the packing is maintained in sealing relation by a follower ring, or gland, progressively pressed into the box by a flanged cap or packing nut as the packing wears to maintain a desired compression of the packing. The shaft must have a smooth surface so that it does not wear away the packing; even so the pressure of the packing considerably increases the force required to rotate the shaft or otherwise move the shaft. A stuffing box even under ideal conditions, does not stop fluid from leaking out and, in fact, proper operation of the stuffing box is in many instances facilitated by a small amount of leakage through the stuffing box, particularly where the fluid which is allowed to leak, whether it is the fluid in the process which is allowed to leak out or a fluid purposely introduced to the stuffing box to leak into the process, is a good lubricant.
In applications where it is desirable to prevent any loss of fluid, and innocuous fluid is to be introduced to the stuffing box, a lantern gland can be used advantageously in the stuffing box. Usually, a lantern gland is a ring adapted to receive the shaft where the lantern gland/shaft assembly is received in the chamber of the stuffing box with packing on either side of the lantern gland. In some previous arrangements, the lantern ring has been of "H" shape in cross section with holes drilled through the bar of the "H" in a direction perpendicular to the axis of the shaft where the inner periphery of the ring receives the shaft and the outer periphery of the ring engages the inner surface of the stuffing box. The wall of the chamber of the stuffing box carries a conduit which takes fluid to or from the lantern ring. For example, an innocuous fluid can be supplied to the lantern ring to flow both ways along the shaft from the lantern ring and through the packing. Alternatively, in some applications, a vacuum is applied to the stuffing box conduit to remove fluid flowing to the lantern ring.
A lantern ring is also used to provide access for a fluid to be used to flush abrasive particles forward from the stuffing box into the process to prevent the particles from reaching the packing where they would destroy the packing and/or damage the shaft. The fluid introduced by means of a lantern ring is also useful to cool the shaft and packing during operation of the device associated with the shaft.
In present lantern rings as previously described and shown in U.S. Pat. No. 1,830,286 Moore where the fluid introduced to the lantern gland flows through the holes in the bar of the ring and thence both inwardly and outwardly from the lantern ring so that some fluid flushes forward to prevent entry of process fluid and abrasive particles into the stuffing box and some fluid flows rearward and is lost out the rear of the stuffing box. The fluid is generally supplied to the lantern gland at an elevated pressure so that the fluid lost from the rear of the stuffing box represents a loss of the value of the fluid as well as a loss of the energy required to supply the fluid to the lantern ring. Heretofore to attempt to minimize this loss, the packing nut or follower has been tightened to the greatest extent possible while still permitting acceptable operation. However, the greater compression of the packing naturally results in greater frictional heat generation and increased probability of damage to the shaft and packing.
No lantern ring has heretofore been provided to maximize fluid flow in one direction from the lantern ring while selectively reducing the rate of fluid flow from the ring along the shaft in an opposite direction, without excessive compression of the packing.